Conventional weapons such as rifles and guns use gunpowder or cordite as the explosive material to propel ammunition. Such explosive materials provide a violent expansion of gases and the liberation of relatively large amounts of thermal energy to achieve propulsion of the ammunition. There are a number of disadvantages associated with such conventional weapons. Firstly, they are highly inefficient in energy transferral from the explosive material to the projectile velocity of the ammunition. In many instances only 20-40% of the energy released by the exploding material is transferred to the projectile velocity.
A number of other disadvantages associated with conventional guns and rifles are the emission of large amounts of thermal energy (heat) and noise that can be easily detected with and without the aid of conventional detection equipment. Also, due to the large amounts of thermal energy being released the barrel and breech of a conventional gun or rifle must be able to withstand high temperatures and therefore are typically made of steel.
There are known guns that utilise a compressed gas, such as carbon dioxide (CO2) to effect propulsion of a projectile. Such arrangements use CO2 in a gaseous state stored in a canister that is removably attached to the gun. Known guns that use such an arrangement are spear guns and paintball guns. However, such arrangements are not suitable for high velocity weapons of the type used for military purposes.
Attempts have been made in the past to heat the gas propellant of gas powered projectile firing devices. U.S. Pat. No. 5,462,042 (Greenwell) describes a CO2 powered paint ball gun in which CO2 is initially stored in a conventional CO2 cartridge. The initial expansion of the chilled CO2 occurs in an expansion chamber in the form of a passage which passes through the hand grip 16 and may be warmed by the heat of a user's hand. This arrangement is to speed up the heating of the CO2 prior to firing of the gun.
German Patent Application DE 3733-240 (Steyr-Daimler-Punch AG) describes a gun using a liquefied gas propellant. The gun has a heater for heating gas as it passes through a tube towards the propellant chamber. The gas is heated on its way to the propellant chamber to enhance precision of the gun by compensating for temperature changes which affect the liquid-gas propellant.
The above described prior art guns utilise heating arrangements that provide heat to the propellant gas prior to it reaching the propellant chamber, in an attempt to overcome firing problems that may occur at colder ambient temperatures. However, these heating arrangements suffer from the disadvantage that they do not ensure reliable repeated firing of a gun over a wide range of cold ambient temperatures.
The present invention seeks to provide a projectile firing device that overcomes the disadvantages associated with conventional weapons and with known gas powered projectile firing devices as described above. It also seeks to provide a means for other projectile firing applications such as launching low earth orbit satellites and payloads.